Capturing the slow relaxation time of superparamagnetic colloids in time-varying fields

TL;DR

This paper investigates the magnetic relaxation dynamics of superparamagnetic colloids in time-varying fields, revealing unexpectedly long relaxation times and advancing understanding of their behavior in complex magnetic environments.

Contribution

It provides the first measurement of long magnetic relaxation times in superparamagnetic colloids under rotating magnetic fields, highlighting mechanisms beyond previous assumptions.

Findings

Discovery of relaxation times much longer than previously reported

Insights into the magnetic behavior of colloids in complex fields

Measurement of effective potential between colloids under rotation

Abstract

Superparamagnetic colloids present interesting assembly dynamics and propulsion in time-varying magnetic fields due to their magnetic relaxation. However, little is known about the mechanisms governing this magnetic relaxation, which is commonly attributed to the interactions and polydispersity of the ferromagnetic nanoparticles distributed within the colloid. We measure this relaxation from the effective potential between colloids subjected to rotating magnetic fields. Remarkably, our results indicate the presence of magnetic relaxation times much longer than what has been reported, which furthers our understanding of the magnetization of colloids in complex magnetic fields.